1. Field of the Invention
The present invention relates to a paper folding apparatus that folds a large sheet in a bellows shape. The paper folding apparatus is connected to a printer, a copying machine, or a fax machine and used as a folder, a finisher, or a connection assembly having a paper folding function, or used as a single folder or a finisher having a paper folding function.
2. Description of the Related Technology
Generally, when an electronic copying machine capable of copying on large sheets such as A0 and A1 is used, if these large sheets are directly stored or handled, a storage space becomes large and handling thereof is inconvenient. Therefore, large sheets are generally folded to be stored or handled. However, if the sheet folding operation is manually performed, a considerably long time is required, and the time required for folding the sheet can be longer than the time required for copying.
Therefore, there is a system in which a paper folding device capable of automatically folding the sheet is arranged in a sheet ejection route of the copying machine, so that the copied large sheet can be automatically folded continuously. In the paper folding device used in such a system, some devices also have a unit not only for automatically folding the sheet ejected from the copying machine (online operation) but also for folding a sheet already copied and ejected without being folded and a large sheet generated by another image forming apparatus (offline operation).
When folding is actually performed by such a system, in the case of regular paper such as A0 and A1, a predetermined size can be used to perform folding as the size for each fold of the sheet to be folded. However, in the electronic copying machine capable of copying on a large sheet, copy can be made on a long sheet having a sub scanning length of several meters, and folding is required for such an irregular long sheet.
A paper folding apparatus described in Japanese Patent Application Laid-open No. H5-238635 folds sheets other than the regular sheets into a specified size by automatically adjusting a folding length of each folding section. Japanese Patent Application Laid-open No. H11-349218 discloses a folding method and a mechanism for forming folds in good order in a desired folding mode, and Japanese Patent Application Laid-open No. 2004-67266 discloses a paper folding device that prevents an unnecessary fold from being formed when a folded sheet is ejected. Japanese Patent Application Laid-open No. 2006-335500, which is proposed by the present inventor, discloses a paper folding apparatus that reduces a difference in the folding size even when a large sheet with the end thereof is curled.
When the regular sheet is folded, the sheet can be folded in a specified finished size by folding the sheet with a predetermined length. In the case of the irregular sheet, the sheet can protrude from the specified finished size. However, even if it is tried to fold the sheet without the protruded portion, the sheet cannot be folded in a short width of from 2 to 30 millimeters (mm) smaller than a minimum folding width, due to a mechanical restriction of the paper folding apparatus (foldable minimum folding width). Even if there is no protruded portion, the number of folds becomes an odd or even number, and therefore the finished state varies according to the size of the original sheet.
Generally, it is preferable that the sheet is folded in a specified finished size (in most cases, A4), and the folded sheet with the protruded portion is not desirable. Further, an original large sheet to be copied and folded is a drawing in most cases, it is desired that the sheet is folded with a title block being on an outside. The title block of the drawing is normally on a right bottom position when the sheet is placed sideways. As shown in FIG. 9A, when the sheet is folded from the left side, designating the first fold as the mountain fold, if the number of folds is an even number, the title block is on the outside (FIG. 9B). However, when the number is an odd number, the title block is on an inside (FIG. 9C), which is not desirable. That is, it is desired to set the upside of the last fold as the outside of the sheet.
To avoid these problems, as one method, in a system having an electronic copying machine capable of cutting a rolled sheet in an arbitrary length and copying on the sheet, the sheet length is appropriately adjusted to a cut length of the rolled sheet set according to a folding condition, so that there is no protruded portion or folding is finished always with even number of folds.
The paper folding apparatus described in Japanese Patent Application Laid-open No. H5-238635 proposes a method in which a detected length of the sheet to be folded is compared with a standard sheet length for each folding pattern to obtain correction data, and the folding size of a certain fold to be folded is corrected according to the correction data, so that even a sheet having an irregular size can be folded in a specified finished size.
By using such methods, even in the case of the irregular sheet, the finished size is always uniform. However, in the case of the method in which the cut length of the rolled sheet is adjusted, a sheet having an unintended copy size is output, and a portion where the length is adjusted becomes a blank space, which is not the original image, thereby making the copy unnatural. Further, the effect cannot be obtained with respect to an irregular sheet output by another system.
In the paper folding apparatus described in Japanese Patent Application Laid-open No. H5-238635, the correction data is obtained by comparing a standard sheet length, which is a regular sheet size, with a detected running sheet length, which is an irregular sheet size to be actually folded, is added to a corrected part, which is the fold to be corrected, so that a specified finished size is obtained. However, when the correction data is for a size equal to or smaller than the standard size of the corrected part, or when the size obtained by adding the correction data to the standard size of the corrected part protrudes from the finished size, the same effect cannot be demonstrated evenly with respect to all sizes of irregular sheet.